1. Field of the Invention
This invention relates in general to a compressed gas sampling device and more specifically involves a manifold and valving device for taking plenum and filter samples from a wide variety of compressed gas sources under actual working conditions.
2. Description of the Related Art
Gas from compressed gas sources is sampled periodically to determine its composition and purity. Periodic sampling is particularly important where the compressed gas is to be used for human respiration, such as in scuba diving. Compressed gas may contain solid contaminants such as dirt, grime, or metal filings which can foul or completely jam a regulator or solid contaminants such as oil mist which can damage a person's lungs and also cause anoxia and death. Gaseous contaminants, such as carbon monoxide, may also cause anoxia, death or severe lung or nerve damage.
Typically, gas compressor output is sampled in the field by non-technical personnel using a field kit. The typical sampling of a gas compressor includes obtaining a plenum sample, i.e. a sample of the compressed gas output in a sampling bomb, and obtaining a filter sample, i.e. passing a known volume of the compressed gas output thru a filter device including a filter so that solid contaminants are trapped in the filter. The filter sample and the plenum sample are commonly sent to a laboratory where the filter is examined for solid contaminants and the plenum is analysed, such as by gas chromatography.
A wide variety of compressors are in use and they vary greatly in their capacity, i.e. in the volume of gas output and in the pressure of that volume. For example, typical low volume/high pressure compressors, such as for diving, output 10-20 SCFM at 3,000 PSI. Small compressors may output a very small volume, for example 3 SCFM or less. A typical large volume/low pressure compressor produces 60-200 SCFM at 225 PSI.
There are a number of disadvantages in conventional compressed gas sampling devices.
Because conventional sampling devices only operate effectively over a small pressure and volume range, a wide variety of sampling devices are in use corresponding to the wide variety of compressor outputs. Therefore, it is desirable to have a single sampling device that can be used for a wide variety of compressors.
Some conventional sampling devices control the pressure to the device by use of a regulator or other throttling device or critical orifices placed in the gas stream before the sampling device. Such devices present impinging surfaces, thereby trapping solid contaminants such that they do not reach the filter. Therefore, it is desirable to have a sampling device that has no front regulator or throttling device so that solid contaminants reach the analytical filter.
The amount of carbon monoxide and film mist in compressor output may be largely dependent on how hard the compressor is working. Many conventional sampling devices do not sample a compressor under actual working conditions. Therefore, it is desirable to have a sampling device that samples the gas output of a compressor under actual working conditions.